Positive electrode for metal air battery, metal air battery including the same, and method of preparing the positive electrode for metal air battery

ABSTRACT

A positive electrode for a lithium battery includes a lithium salt, a carbonaceous material, and a coating on a surface of the carbonaceous material, the coating including a polymer electrolyte including a hydrophilic material and a hydrophobic material, wherein a portion of the polymer electrolyte is anchored to the surface of the carbonaceous material by a chemical bond.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 15/667,753 filed on Aug. 3, 2017 in the United States Patent andTrademark Office, issued as U.S. Pat. No. 10,593,950, and claimspriority to and the benefit of Korean Patent Application No.10-2016-0100881, filed on Aug. 8, 2016, and Korean Patent ApplicationNo. 10-2017-0069076, filed on Jun. 2, 2017, in the Korean IntellectualProperty Office, and all the benefits accruing therefrom under 35 U.S.C.§ 119, the contents of which are incorporated herein in their entiretyby reference.

BACKGROUND 1. Field

An aspect of the present disclosure relates to a positive electrode fora metal air battery, a metal air battery including the same, and amethod of preparing the positive electrode for a metal air battery.

2. Description of the Related Art

A metal air battery, for example, a lithium air battery, generallyincludes a negative electrode capable of intercalation anddeintercalation of lithium ions, a positive electrode (air electrode) inwhich oxidation and reduction of oxygen occurs using oxygen as an activematerial, and a separator interposed between the negative electrode andthe positive electrode.

A lithium air battery may have a theoretical energy density per unitweight of 3,500 watt hours per kilogram (Wh/kg) or greater, which isabout ten times greater than that of a lithium ion battery.

However, there is still a need to develop a positive electrode for ametal air battery, a metal air battery including the same, and a methodof preparing the positive electrode for a metal air battery having animproved energy density per unit weight.

SUMMARY

Provided is a positive electrode for a metal air battery including acarbonaceous material having a polymer electrolyte layer coated on asurface thereof and including a polymer electrolyte including at leastone hydrophilic material and at least one hydrophobic material.

Provided is a metal air battery including the positive electrode.

Provided is a method of preparing the positive electrode for a metal airbattery.

According to an aspect of an example embodiment, a positive electrodefor a metal air battery includes a lithium salt, a carbonaceousmaterial, and a coating on a surface of the carbonaceous material, thecoating including a polymer electrolyte including a hydrophilic materialand a hydrophobic material, wherein a part of the polymer electrolyte isanchored to the surface of the carbonaceous material by a chemical bond.

According to an aspect of another example embodiment, a metal airbattery may include a negative electrode including lithium or a lithiumalloy, the positive electrode, and a separator disposed between thenegative electrode and the positive electrode.

According to an aspect of another example embodiment, a method ofpreparing a positive electrode for a metal air battery includescombining the carbonaceous material, the polymer electrolyte, a lithiumsalt, and a solvent, dispersing the carbonaceous material, the polymerelectrolyte, and the lithium salt in the solvent to prepare adispersion, and drying the dispersion.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented example embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the example embodiments,taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic diagram of a structure of a positive electrode inwhich carbonaceous materials are coated with polymer electrolyte layeraccording to an example embodiment;

FIG. 2 is a schematic diagram for describing a method of preparing apositive electrode for a metal air battery, according to an exampleembodiment;

FIG. 3 is a schematic diagram of a structure of a lithium air battery,according to an example embodiment;

FIG. 4A is a transmission electron microscope (TEM) image of acarbonaceous material coated with a polymer electrolyte layer, preparedaccording to Example 1;

FIGS. 4B and 4C are TEM images of a carbonaceous material coated with apolymer electrolyte layer, prepared according to Example 2;

FIG. 5 is a graph of weight (percentage, %) versus temperature (degreesCelsius, ° C.) showing the thermal gravimetric analysis (TGA) graph of apolymer electrolyte layer of the carbonaceous material coated with thepolymer electrolyte layer, prepared according to Example 1;

FIGS. 6A and 6B are graphs of intensity (arbitrary units, a.u.) versusbinding energy (electron volts, eV) showing, respectively, a C1sspectrum and an O1s spectrum obtained by X-ray photoelectronspectroscopy (XPS) of a carbonaceous material coated with a polymerelectrolyte layer, prepared according to Example 2; and

FIGS. 7A and 7B are graphs of voltage (V) versus capacity (milliamperehours, mAh) of the first discharge cycle of a lithium air batteryprepared according to Examples 3 and 4.

DETAILED DESCRIPTION

Reference will now be made in detail to example embodiments, which areillustrated in the accompanying drawings, wherein like referencenumerals refer to like elements throughout. In this regard, the presentexample embodiments may have different forms and should not be construedas being limited to the descriptions set forth herein. Accordingly, theexample embodiments are merely described below, by referring to thefigures, to explain aspects. As used herein, the term “and/or” includesany and all combinations of one or more of the associated listed items.“Or” means “and/or.” Expressions such as “at least one of,” whenpreceding a list of elements, modify the entire list of elements and donot modify the individual elements of the list.

It will be understood that when an element is referred to as being “on”another element, it can be directly on the other element or interveningelements may be present therebetween. In contrast, when an element isreferred to as being “directly on” another element, there are nointervening elements present.

It will be understood that, although the terms “first,” “second,”“third,” etc. may be used herein to describe various elements,components, regions, layers, and/or sections, these elements,components, regions, layers, and/or sections should not be limited bythese terms. These terms are only used to distinguish one element,component, region, layer, or section from another element, component,region, layer, or section. Thus, “a first element,” “component,”“region,” “layer,” or “section” discussed below could be termed a secondelement, component, region, layer or section without departing from theteachings herein.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a,” “an,” and “the” are intended to include the pluralforms, including “at least one,” unless the content clearly indicatesotherwise. “At least one” is not to be construed as limiting “a” or“an.” It will be further understood that the terms “comprises” and/or“comprising,” or “includes” and/or “including” when used in thisspecification, specify the presence of stated features, regions,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components, and/orgroups thereof.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper,” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

“About” or “approximately” as used herein is inclusive of the statedvalue and means within an acceptable range of deviation for theparticular value as determined by one of ordinary skill in the art,considering the measurement in question and the error associated withmeasurement of the particular quantity (i.e., the limitations of themeasurement system). For example, “about” can mean within one or morestandard deviations, or within ±30%, 20%, 10% or 5% of the stated value.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

Exemplary embodiments are described herein with reference to crosssection illustrations that are schematic illustrations of idealizedembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, embodiments described herein should not beconstrued as limited to the particular shapes of regions as illustratedherein but are to include deviations in shapes that result, for example,from manufacturing. For example, a region illustrated or described asflat may, have rough and/or nonlinear features. Moreover, sharp anglesthat are illustrated may be rounded. Thus, the regions illustrated inthe figures are schematic in nature and their shapes are not intended toillustrate the precise shape of a region and are not intended to limitthe scope of the present claims.

Hereinafter, a positive electrode for a metal air battery, a metal airbattery including the same, and a method of preparing the positiveelectrode for a metal air battery according to example embodiments willbe described in detail with reference to the drawings.

A metal air battery, for example, a lithium air battery, may include anegative electrode capable of intercalation/deintercalation of lithiumions, a positive electrode using oxygen as an active material, and anelectrolyte capable of transporting the lithium ions. The lithium airbattery advantageously has a high theoretical energy density per unitweight since oxygen is not stored in the lithium air battery.

In general, a lithium air battery may include an electrolyte to obtain apathway of lithium ions. However, the energy density per unit weight maydecrease when a lithium air battery includes an excess of an electrolytein comparison with a carbonaceous material of the positive electrode(air electrode).

In order to prevent a decrease in energy density per unit weight, thereis therefore a need to develop a positive electrode for a metal airbattery having an improved energy density per unit weight.

As an electrolyte, the lithium air battery may include an aqueouselectrolyte or a nonaqueous electrolyte. However, the aqueouselectrolyte may cause serious corrosion in a lithium air battery due tocontact between a lithium negative electrode and the aqueouselectrolyte. As a result, extensive research has been conducted intodeveloping improved nonaqueous electrolytes.

Examples of the nonaqueous electrolyte may include an ionic liquid or anorganic liquid electrolyte. Examples of the organic liquid electrolytemay include a carbonate, an ether, a sulfone, N,N-dimethylsulfoxide(DMSO), N,N-dimethylacetamide (DMAC), or the like.

The use of the nonaqueous electrolyte as the electrolyte may cause areaction mechanism represented by Reaction Scheme 1 below.4Li+O₂↔2Li₂O E°=2.91 V2Li+O₂↔Li₂O₂ E°=3.10 V  Reaction Scheme 1

During discharge, lithium introduced from the negative electrode reactswith oxygen introduced from the positive electrode (air electrode) togenerate lithium oxide and reduce oxygen (oxygen reduction reaction(ORR)). During charge, the lithium oxide is reduced, and oxygen isoxidized to generate oxygen gas (oxygen evolution reaction (OER)).According to Reaction Scheme 1, Li₂O₂ is precipitated in pores of thepositive electrode (air electrode) during discharge, and a capacity ofthe lithium air battery increases as a contact area between theelectrolyte and the positive electrode (air electrode) increases.

The positive electrode (air electrode) may include a carbonaceousmaterial having a large specific surface area and a large pore volume.However, due to the large pore volume, an increased amount of theelectrolyte is used in the metal air battery. When the amount of theelectrolyte is greater than the amount of the carbonaceous material, thespace for discharge products is occupied by an excess of theelectrolyte. As a result, generation of the discharge products isinhibited, and thus a weight of the metal air battery may increase andan energy density per unit weight of the metal air battery may decrease.

The positive electrode for a metal air battery according to an exampleembodiment includes: a lithium salt; a carbonaceous material; and acoating on a surface of the carbonaceous material, the coating includinga polymer electrolyte layer including a polymer electrolyte including atleast one type of hydrophilic material and at least one type ofhydrophobic material. A portion of the polymer electrolyte may beanchored to the surface of the carbonaceous material via a chemicalbond, e.g., a noncovalent bond or a covalent bond.

Throughout the specification, the terms “hydrophilic” and “hydrophobic”are understood as relative concepts.

Throughout the specification, the term “hydrophilic” refers to“hydrophilic properties of a surface of a material, and the term“hydrophobic” refers to hydrophobic properties of a surface of amaterial.” As used herein, the terms “hydrophilic material” and“hydrophobic material” are distinguished from each other based on thewettability of a surface of the material by water. Wettability of thesurface of the material by water may be quantitatively analyzed using acontact angle between the material and water.

The term “contact angle with water” refers to an angle between a surfaceof water and a surface of a material when the water reaches athermodynamic equilibrium with a surface of the material. For example,the contact angle with water may be acquired by dropping a predeterminedvolume of water on a substrate coated with a material and measuring atangent angle of a line between a point of contact between the substrateand the water droplet and a contact point of the surface of thematerial. For example, the contact angle with water may be theoreticallydefined by Young's Equation below.

cos θ_(Y)γ_(s) v−

|VC  (1)

In the equation (1) above,

,

, and

are, respectively, interfacial tensions between liquid and gaseousphases, solid and gaseous phases, and solid and liquid phases, and θ_(Y)is a contact angle.

The contact angle with water may be measured using various known methodssuch as a Telescope-Goniometer, captive bubble method, tilting platemethod, Wilhelmy balance method, capillary tube method, static sessiledroplet method, or ACCUDYNE TEST™ kit.

The polymer electrolyte may include a hydrophilic material and ahydrophobic material, each having a contact angle with water, whereinthe difference between the contact angle of the hydrophilic material andthe contact angle of the hydrophobic material is 5° or greater. Thecontact angle with water of the hydrophilic material may be about 0° toabout 70°. The contact angle with water of the hydrophobic material maybe 70° or greater. Unless stated otherwise, the contact angle isdetermined at 20° C.

The contact angle with water is inversely correlated to the solubilityof the material in water. That is, the contact angle with water maydecrease as solubility in water increases, and the contact angle withwater may increase as solubility in water decreases. Thus, a hydrophilicmaterial has a higher solubility in water than a hydrophobic material.

For example, polyethylene glycol, as a hydrophilic material, having amolecular weight of 4,000 Daltons (Da) is highly soluble in water with asolubility of 66% (w/w) at 20° C. In comparison, for example,polypropylene glycol, as a hydrophobic material, having a molecularweight of 4,000 Da is less soluble in water with a solubility of lessthan 0.01% (w/w) at 20° C. Thus, for example, for a polyethyleneglycol-polypropylene glycol-polyethylene glycol block copolymer, apolypropylene glycol block that is a hydrophobic material having a lowsolubility in water may be disposed at inner positions of the blockcopolymer and a polyethylene glycol block that is a hydrophilic materialhaving a relatively high solubility in water may be disposed at outerpositions of the block copolymer, in accordance with a concentration ofthe polymer in a water solution.

The noncovalent bond refers to a relatively weak bond formed between thesurface of the carbonaceous material and the polymer electrolyte. Thenoncovalent bond may be, for example, a hydrogen bond, a Van der Waalsbond, a charge transfer, a dipole-dipole interaction, a pi-pi (π-π)stacking interaction, or the like. The noncovalent bond may be formed bybonding the polymer electrolyte to the carbonaceous material withoutaltering the surface of the carbonaceous material.

The covalent bond refers to a bond formed by a reaction between areactive functional group directly attached to the surface of thecarbonaceous material and a functional group on the polymer electrolyte.For example, the reactive functional group directly attached to thesurface of the carbonaceous material may be a —COOH group, a —COH group,or a —OH group. For example, the covalent bond may be formed byoxidation, halogenation, cycloaddition, radical addition, thiolation, orthe like. For example, the covalent bond may be formed by introducing areactive functional group such as a carboxyl group (—COOH) on thesurface of the carbonaceous material via oxidation by acid treatment,and then forming the covalent bond between the surface of thecarbonaceous material and the polymer electrolyte by using a functionalgroup of the polymer electrolyte having an ethylene oxide block having aside chain such as an amino group (—NH₂) (e.g., a polyethylene oxide(PEO)-b-polypropylene oxide (PPO)-b-polyethylene oxide (PEO) triblockcopolymer).

The term “anchored” refers to a state in which a material is attached ona surface of a support and a portion of the material attached to thesurface is fixed to the surface. The other portions of the material notattached to the surface of the support may be mobilized or unfixed.

FIG. 1 is a schematic diagram of a structure of a positive electrode inwhich carbonaceous material are coated with polymer electrolyte layersaccording to an example embodiment.

Referring to FIG. 1, the positive electrode has a structure in which apolymer electrolyte coating layer is formed on the surface of acarbonaceous material 1. The polymer electrolyte coating layer includesa polymer electrolyte including a hydrophobic material 2 and ahydrophilic material 3. Voids are present among a plurality of thecarbonaceous materials 1 respectively having the polymer electrolytecoating layer.

Since the positive electrode for a metal air battery according to anexample embodiment includes the polymer electrolyte coating layerincluding the polymer electrolyte including the at least one type ofhydrophilic material and the at least one type of hydrophobic materialcoated on the surface of the carbonaceous material, an amount of theelectrolyte may be reduced. In addition, since a portion of the polymerelectrolyte is anchored to the surface of the carbonaceous material, vianoncovalent or covalent bonds, the integrity of the polymer electrolytecoating layer may be maintained during repeated charging and dischargingof the metal air battery. As a result, the metal air battery may have areduced weight and an increased energy density per unit weight.

All, or a portion of, the at least one type of hydrophobic material ofthe polymer electrolyte may be anchored to the surface of thecarbonaceous material via noncovalent bonds. Since the surface of thecarbonaceous material is hydrophobic, all or a portion of thehydrophobic material of the polymer electrolyte may be easily anchoredto the surface of the carbonaceous material due to the high affinitybetween the carbonaceous material and the hydrophobic material of thepolymer electrolyte.

All, or a portion of, the hydrophobic material of the polymerelectrolyte may include a hydrophobic repeating unit and/or ahydrophobic functional group.

Examples of the hydrophobic repeating unit may include butyl acrylate,2-ethylhexyl acrylate, methacrylate, benzyl methacrylate, butylmethacrylate, tert-butyl methacrylate, cyclohexyl methacrylate,2-ethylhexyl methacrylate, hexadecyl methacrylate, hexyl methacrylate,isobutyl methacrylate, isopropyl methacrylate, methyl methacrylate,octadecyl methacrylate, tetrahydrofurfuryl methacrylate, acrylonitrile,maleic anhydride, styrene, propylene glycol, propylene oxide, butene,1-decene, dicyclopentadiene, isobutylene, 4-methyl-1-pentene, ethylene,propylene, ethylene adipate, ethylene succinate, ethylene terephthalate,2-ethyl-1,3-hexanediol sebacate, vinyl acetate, vinyl cinnamate, vinylstearate, tetrahydrofuran, and any copolymers thereof.

Examples of the hydrophobic functional group may include a hydroxylgroup, a methyl group, a carbonyl group, a carboxyl group, an aminogroup, a phosphate group, a mercapto group, and a combination thereof.

The hydrophobic repeating unit and/or the hydrophobic functional groupmay be located as a backbone and/or as a side chain of the polymerelectrolyte.

All or a portion of the hydrophobic material of the polymer electrolyteincluded in the polymer electrolyte layer may be adsorbed to the surfaceof the carbonaceous material, for example, via Van der Waals'interactions. Due to such adsorption, there is no need to induce areaction between the hydrophobic material and the surface of thecarbonaceous material, and thus the surface of the carbonaceous materialmay be functionalized with the hydrophobic material and retain theintrinsic properties of the carbonaceous material. Therefore, lithiumion conductivity of the metal air battery may be maintained withoutbeing reduced.

The polymer electrolyte may include a crosslinked polymer electrolyte.The crosslinked polymer electrolyte may anchor the polymer electrolytecoating layer to the surface of the carbonaceous material more firmly.Thus, the amount of the electrolyte may be considerably reduced. As aresult, the metal air battery may have a reduced weight and an increasedenergy density per unit weight.

For example, the polymer electrolyte of the polymer electrolyte layermay include a block copolymer comprised of a block of the hydrophobicmaterial (i.e., hydrophobic block) and a block of the hydrophilicmaterial (i.e., hydrophilic block).

The hydrophobic block is the same as the hydrophobic repeating unitdescribed above.

Examples of the hydrophilic block may include ethylene glycol, ethyleneoxide, N-isopropylacrylamide, 2-oxazoline, 2-ethyl-2-oxazoline,ethyleneimine, sulfopropyl acrylate, 2-hydroxypropyl methacrylate, vinylalcohol, vinyl pyrrolidone, and any copolymers thereof.

The hydrophobic block of the block copolymer may be anchored to thesurface of the carbonaceous material, and the hydrophilic block may bearranged on the surface of the carbonaceous material away from thesurface of the carbonaceous material. For example, since the hydrophobicblock of the block copolymer is adsorbed to the surface of thecarbonaceous material via Van der Waals' interactions, and thehydrophilic block is arranged on the surface of the carbonaceousmaterial away from the surface of the carbonaceous material, lithiumions may be efficiently conducted. An example of this structure is shownin FIGS. 2 and 4B.

For example, the block copolymer may include propylene oxide (orpropylene glycol) as an example of the hydrophobic block and ethyleneoxide (or ethylene glycol) as an example of the hydrophilic block. Thisclassification of hydrophobic versus hydrophilic is based on therelative concepts previously described above.

In the block copolymer, propylene oxide (or propylene glycol) as ahydrophobic block is adsorbed to the surface of the carbonaceousmaterial via Van der Waals' interactions and ethylene oxide (or ethyleneglycol) as a hydrophilic block is arranged outward from the surface ofthe carbonaceous material. Then, for example, a polymer electrolyteincluding polyethylene oxide (or polyethylene glycol) crosslinked withadjacent CH. radicals, which are formed from CH₂ of the hydrophilicblock of ethylene oxide (or ethylene glycol) via ultraviolet (UV) lightcrosslinking (or thermal crosslinking) using a radical agent such as anUV initiator, as shown in Reaction Scheme 2 below, and polypropyleneoxide (or polypropylene glycol) mostly uncrosslinked may be formed.

The block copolymer may include two or more different polymerizablemonomer blocks. For example, the block copolymer may include two orthree different polymerizable monomer blocks.

A number average molecular weight Mn of the hydrophilic block of theblock copolymer may be about 500 Da to about 20,000 Da. For example, thenumber average molecular weight Mn of the hydrophilic block of the blockcopolymer may be about 500 Da to about 18,000 Da, for example, about 500Da to about 16,000 Da, for example, about 500 Da to about 14,000 Da, forexample, about 500 Da to about 12,000 Da, for example, about 500 Da toabout 10,000 Da, for example, about 500 Da to about 9,000 Da, forexample, about 500 Da to about 8,000 Da, for example, about 500 Da toabout 7,000 Da, for example, about 500 Da to about 6,000 Da, forexample, about 500 Da to about 5,000 Da, for example, about 600 Da toabout 5,000 Da, for example, about 700 Da to about 5,000 Da, and forexample, about 800 Da to about 5,000 Da. If the number average molecularweight Mn of the hydrophilic block of the block copolymer is withinthese ranges, the hydrophilic blocks do not agglomerate but aredispersed, resulting in improvement of lithium ion conductivity of themetal air battery.

The hydrophilic block may be a polymer block having a lithium ionconductive group as a side chain. The lithium ion conductive group is ahydrophilic group. Examples of the lithium ion conductive group as theside chain may include —SO₃ ⁻, —COO⁻, —(CF₃SO₂)₂N⁻ (hereinafter,referred to as TFSI anion), —(FSO₂)₂N⁻ (hereinafter, referred to as FSIanion), —SO₂N SO₂CF₃, —SO₂N SO₂CF₂CF₃, —SO₂C₆H₄COO⁻, —C₆H₃(SO₂NH₂)COO⁻,—CH(COO⁻)CH₂COO⁻, —C6H3(OH)COO⁻, —C₆H₂(NO₂)₂COO⁻, or —CH₂C(CH₃)₂COO⁻.

The polymer block having a lithium ion conductive group as a side chainmay be, for example, a polyacrylate block functionalized with TFSI-anionor FSI-anion or a poly(meth)acrylate block functionalized withTFSI-anion or FSI-anion. If the lithium ion conductive group is includedas a side chain, lithium ion conductivity may be improved by easilysecuring the mobility of lithium ions.

The block copolymer may be an uncrosslinked or crosslinked blockcopolymer.

For example, the block copolymer may include a polyethyleneglycol-b-polypropylene glycol diblock copolymer, a polyethyleneoxide-b-polypropylene oxide diblock copolymer, apolystyrene-b-polyethylene glycol diblock copolymer, apolystyrene-b-polyethylene oxide diblock copolymer, apolystyrene-b-poly(4-vinyl pyridine) diblock copolymer, apolystyrene-b-poly(meth)acrylate diblock copolymer, apolystyrene-b-poly(meth)acrylate diblock copolymer functionalized withTFSI⁻ anion, a polystyrene-b-poly(meth)acrylate diblock copolymerfunctionalized with FSI⁻ anion, a polyethylene glycol-b-polypropyleneglycol-b-polyethylene glycol triblock copolymer, a polyethyleneoxide-b-polypropylene oxide-b-polyethylene oxide triblock copolymer, apolyethylene glycol-b-polystyrene-b-polyethylene glycol triblockcopolymer, a polyethylene oxide-b-polystyrene-b-polyethylene oxidetriblock copolymer, or a combination thereof.

For example, the block copolymer may include a crosslinked polyethyleneglycol-b-polypropylene glycol diblock copolymer, a crosslinkedpolyethylene oxide-b-polypropylene oxide diblock copolymer, acrosslinked polystyrene-b-polyethylene glycol diblock copolymer, acrosslinked polystyrene-b-polyethylene oxide diblock copolymer, acrosslinked polystyrene-b-poly(meth)acrylate diblock copolymerfunctionalized with TFSI⁻ anion, a crosslinkedpolystyrene-b-poly(meth)acrylate diblock copolymer functionalized withFSI⁻ anion, a crosslinked polyethylene glycol-b-polypropyleneglycol-b-polyethylene glycol triblock copolymer, a crosslinkedpolyethylene oxide-b-polypropylene oxide-b-polyethylene oxide triblockcopolymer, a crosslinked polyethyleneglycol-b-polystyrene-b-polyethylene glycol triblock copolymer, acrosslinked polyethylene oxide-b-polystyrene-b-polyethylene oxidetriblock copolymer, or a combination thereof.

For example, the block copolymer may include a crosslinked polyethyleneglycol-b-polypropylene glycol diblock copolymer, a crosslinkedpolyethylene oxide-b-polypropylene oxide diblock copolymer, acrosslinked polystyrene-b-polyethylene glycol diblock copolymer, acrosslinked polystyrene-b-polyethylene oxide diblock copolymer, acrosslinked polyethylene glycol-b-polypropylene glycol-b-polyethyleneglycol triblock copolymer, a crosslinked polyethyleneoxide-b-polypropylene oxide-b-polyethylene oxide triblock copolymer, acrosslinked polyethylene glycol-b-polystyrene-b-polyethylene glycoltriblock copolymer, a crosslinked polyethyleneoxide-b-polystyrene-b-polyethylene oxide triblock copolymer, or acombination thereof.

The number average molecular weight Mn of the block copolymer may beabout 3,000 Da to about 60,000 Da. For example, the number averagemolecular weight Mn of the block copolymer may be about 3,000 Da toabout 55,000 Da, for example, about 3,000 Da to about 50,000 Da, forexample, about 3,000 Da to about 45,000 Da, for example, about 3,000 Dato about 40,000 Da, for example, about 3,000 Da to about 35,000 Da, forexample, about 3,000 Da to about 30,000 Da, for example, about 3,000 Dato about 25,000 Da, for example, about 3,000 Da to about 20,000 Da, forexample, about 3,500 Da to about 20,000 Da, for example, about 4,000 Dato about 20,000 Da, for example, about 4,500 Da to about 20,000 Da, andfor example, about 5,000 Da to about 20,000 Da. If the number averagemolecular weight Mn of the block copolymer is within these ranges,lithium ion conductivity may be increased with high elasticity andwithout increasing crystallinity.

An amount of the polymer electrolyte may be about 10 parts by weight toabout 300 parts by weight based on 100 parts by weight of thecarbonaceous material. If the amount of the polymer electrolyte iswithin this range, a lithium battery may have sufficient lithium ionconductivity and high energy density per unit weight.

A thickness of the polymer electrolyte layer may be about 1 nanometer(nm) to about 30 nm. For example, the thickness of the polymerelectrolyte layer may be about 1 nm to about 28 nm, for example, about 1nm to about 26 nm, for example, about 1 nm to about 24 nm, for example,about 1 nm to about 22 nm, for example, about 1 nm to about 20 nm, forexample, about 1 nm to about 18 nm, for example, about 1 nm to about 16nm, for example, about 1 nm to about 14 nm, for example, about 1 nm toabout 12 nm, and for example, about 1 nm to about 10 nm. When thethickness of the polymer electrolyte layer is within these ranges,sufficient lithium ion conductivity and high energy density per unitweight may be obtained.

The polymer electrolyte layer may be electrochemically stable withrespect to lithium in a charge/discharge voltage range of about 1.4 volt(V) to about 4.5 V. For example, the polymer electrolyte layer may beelectrochemically stable with respect to lithium in a charge/dischargevoltage range of about 1.5 V to about 4.5 V.

The carbonaceous material may have a porous carbon structure. All or aportion of the carbonaceous material may have a porous carbon structure.For example, the porous carbon structure may be mesoporous. Thecarbonaceous material may have a sufficient specific surface area andmay efficiently transport electrons thereon.

For example, the carbonaceous material may include carbon nanotubes,carbon nanoparticles, carbon nanofibers, carbon nanosheets, carbonnanorods, carbon nanobelts, graphene, graphene oxide, carbon aerogel,inverse opal carbon, any mixture thereof, or any composite thereof. Forexample, the carbonaceous material may be carbon nanotubes, carbonnanoparticles, or any composite thereof. For example, the composite maybe a composite in which carbon nanoparticles are disposed on the surfaceof carbon nanotubes.

For example, the carbonaceous material may be carbon nanotubes. Thecarbon nanotubes may be single-walled carbon nanotubes (SWCNTs),double-walled carbon nanotubes (DWCNTs), multi-walled carbon nanotubes(MWCNTs), rope carbon nanotubes, or any combination thereof.

The carbonaceous material may be single-walled carbon nanotubes(SWCNTs), double-walled carbon nanotubes (DWCNTs), multi-walled carbonnanotube (MWCNTs), or any combination thereof.

An average aspect ratio (average length/average diameter) of the carbonnanotubes may be about 1 to about 20,000. The average aspect ratio maybe measured by any suitable method, for example, using a transmissionelectron microscope (TEM) image, a high-resolution transmission electronmicroscope (HR-TEM) image, a scanning electron microscope (SEM) image,or a field-emission scanning electron microscope (FE-SEM) image, and/ora measuring device using dynamic light-scattering. When the averageaspect ratio of the carbon nanotubes is within this range, electriccharges are quickly transported from the surface of each nanotube to theinside thereof.

An amount of the carbonaceous material may be about 50 parts by weightto about 80 parts by weight based on 100 parts by weight of the positiveelectrode.

The lithium salt may include at least one of LiPF₆, LiBF₄, LiSbF₆,LiAsF₆, LiN(SO₂C₂F₅)₂, Li(CF₃SO₂)₂N, LiC₄F₉SO₃, LiClO₄, LiAlO₂, LiAlC₄,LiN(C_(x)F_(2x+1)SO₂) (C_(y)F_(2y+1)SO₂) (where x and y are naturalnumbers), LiF, LiBr, LiCl, LiOH, LiI and LiB(C₂O₄)₂ (lithiumbis(oxalato) borate; LiBOB). However, the example embodiment is notlimited thereto, and any compound available as the lithium salt may alsobe used.

An amount of the lithium salt may be about 5 parts by weight to about 60parts by weight based on 100 parts by weight of the positive electrode.When the amount of the lithium salt within this range, sufficientlithium ion conductivity may be obtained.

A molar ratio of the polymer electrolyte monomers of the polymerelectrolyte layer to lithium ions may be about 40:1 to about 3:1. Forexample, the molar ratio of the polymer electrolyte monomers of thepolymer electrolyte layer to lithium ions may be about 20:1 to about10:1. However, the molar ratio of the polymer electrolyte monomers ofthe polymer electrolyte layer to lithium ions is not limited thereto solong as lithium ions and/or electrons are efficiently transported duringcharging and discharging.

The positive electrode may be an air electrode.

A lithium battery according to another example embodiment may be alithium air battery. The lithium air battery may include: a negativeelectrode including lithium or a lithium alloy; the positive electrodeas described above; and a separator disposed between the negativeelectrode and the positive electrode.

FIG. 3 is a schematic diagram illustrating a structure of a lithium airbattery 10 according to an example embodiment.

As illustrated in FIG. 3, the lithium air battery 10 includes a positiveelectrode (air electrode) 15 disposed adjacent to a first currentcollector 14 and using oxygen as an active material, a negativeelectrode 13 disposed adjacent to a second current collector 12 andincluding lithium or a lithium alloy, and a separator 16 interposedbetween the negative electrode 13 and the positive electrode 15. Alithium ion conductive solid electrolyte membrane (not shown) mayfurther be disposed on the surface of the positive electrode (airelectrode) 15 facing the separator 16.

The first current collector 14, which is porous, may also serve as a gasdiffusion layer allowing diffusion of air. A pressing member 19 allowingair to reach the positive electrode (air electrode) 15 may further bedisposed on the first current collector 14. A case 11 comprised of aninsulating resin material is disposed between the positive electrode(air electrode) 15 and the negative electrode 13 to electricallyseparate the air electrode from the negative electrode. Air is suppliedthrough an air inlet 17 a and discharged through an air outlet 17 b. Thelithium air battery 10 may be stored in a stainless steel reactor (notshown).

The positive electrode (air electrode) 15 includes the lithium salt andthe carbonaceous material having a polymer electrolyte layer coated on asurface of the carbonaceous material and including a polymer electrolytecomprised of at least one type of hydrophilic material and at least onetype of hydrophobic material. A portion of the polymer electrolyte maybe anchored to the surface of the carbonaceous material via anoncovalent bond or a covalent bond.

The lithium salt, the polymer electrolyte, the polymer electrolytelayer, the carbonaceous material, and the anchored state of the polymerelectrolyte via a noncovalent or a covalent bond are as described above,and thus a further description thereof will not be given.

The positive electrode (air electrode) 15 may further include an oxygenoxidizing/reducing catalyst. Examples of the oxygen oxidizing/reducingcatalyst may include a noble metal catalyst such as platinum (Pt), gold(Au), silver (Ag), palladium (Pd), ruthenium (Ru), rhodium (Rh), andosmium (Os), an oxide catalyst such as manganese oxide, iron oxide,cobalt oxide, and nickel oxide, or an organometallic catalyst such ascobalt phthalocyanine, without being limited thereto. Any other catalystsuitable for as an oxygen oxidizing/reducing catalyst in the art mayalso be used.

The positive electrode (air electrode) 15 may further include a binder.The binder may include a thermoplastic resin or a thermosetting resin.Examples of the binder may include polyethylene, polypropylene,polytetrafluorethylene (PTFE), polyvinylidene difluoride (PVDF),styrene-butadiene rubber, a tetrafluoroethylene-perfluoroalkylvinylethercopolymer, a vinylidene fluoride-hexafluoropropylene copolymer, avinylidene fluoride-chlorotrifluoroethylene copolymer, anethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, afluorovinylidene-pentafluoropropylene copolymer, apropylene-tetrafluoroethylene copolymer, anethylene-chlorotrifluoroethylene copolymer, a vinylidenefluoride-hexafluoropropylene-tetrafluoroethylene copolymer, a vinylidenefluoride-perfluoromethylvinylether-tetrafluoro ethylene copolymer, andan ethylene-acrylic acid copolymer, each of which may be used alone orin combination with each other, without being limited thereto. Anymaterial available as a binder in the art may also be used.

The second current collector 12 may be any current collector havingelectrical conductivity, without limitation. For example, stainlesssteel, nickel (Ni), copper (Cu), aluminum (Al), iron (Fe), titanium(Ti), carbon (C), or the like may be used. The second current collector12 may have the form of a thin film, a plate, a mesh, and a grid. Forexample, the second current collector 12 may include a copper foil. Thesecond current collector 12 may be fixed to a Teflon case (not shown).

The negative electrode 13 may include lithium or a lithium alloy. Ifdesired, the negative electrode 13 may include a lithium intercalationcompound. However, the negative electrode 13 is not limited thereto, andany lithium-containing material or any compound capable of intercalationand deintercalation of lithium may also be used as the negativeelectrode 13. Examples of the lithium alloy may include an alloy oflithium and aluminum, tin, magnesium, indium, calcium, titanium,vanadium, or a combination thereof. The negative electrode 13determining capacity of the lithium air battery may be a lithium thinfilm.

If desired, the negative electrode 13 may further include a binder. Forexample, the binder may be polyvinylidene fluoride (PVdF) orpolytetrafluoroethylene (PTFE). An amount of the binder may be 30 partsby weight or less, for example, about 1 to about 10 parts by weight,based on 100 parts by weight of the negative electrode 13, without beinglimited thereto.

The separator 16 may have varying compositions when used in the lithiumair battery 10. For example, the separator 16 may be a polymer non-wovenfabric such as a polypropylene non-woven fabric or a polyphenylenesulfide non-woven fabric, or a porous film of an olefin resin such aspolyethylene or polypropylene, used alone or as a combination thereof.

A lithium ion conductive solid electrolyte membrane may further bedisposed on the surface of the positive electrode (air electrode) 15 orthe negative electrode 13. For example, the lithium ion conductive solidelectrolyte membrane may serve as a protective layer to prevent directreaction between impurities included in the electrolyte, such as waterand oxygen, and lithium included in the negative electrode 13. Examplesof the lithium ion conductive solid electrolyte membrane may include aninorganic material such as lithium ion conductive glass, lithium ionconductive crystalline material (e.g., ceramic or glass-ceramic), aninorganic material, or any mixture thereof. However, the lithium ionconductive solid electrolyte membrane is not limited thereto, and anysolid electrolyte membrane having lithium ion conductivity and capableof protecting the positive electrode (air electrode) 15 or the negativeelectrode 13 may also be used. Meanwhile, in consideration of chemicalstability, the lithium ion conductive solid electrolyte membrane may bean oxide.

Examples of the lithium ion conductive crystalline may be Li_(1+x+y)(Al,Ga)_(x)(Ti, Ge)_(2-x)Si_(y)P_(3-y)O₁₂ (where 0≤x≤1 and 0≤y≤1, forexample, 0≤x≤0.4 and 0<y≤0.6 or 0.1≤x≤0.3 and 0.1<y≤0.4). Examples ofthe lithium ion conductive glass-ceramic may includelithium-aluminum-germanium-phosphate (LAGP),lithium-aluminum-titanium-phosphate (LATP), andlithium-aluminum-titanium-silicon-phosphate (LATSP). Also, the lithiumion conductive solid electrolyte membrane may further include aninorganic solid electrolyte, if desired. Examples of the inorganic solidelectrolyte may include Cu₃N, Li₃N, and LiPON. The lithium ionconductive solid electrolyte membrane may be a single-layer ormulti-layer membrane.

The lithium air battery 10 may be prepared as follows.

First, the aforementioned positive electrode (air electrode) 15); thenegative electrode 13 including lithium or a lithium alloy; and theseparator 16 are prepared.

Next, the negative electrode 13 is mounted on one side of a case 11, theseparator 16 is mounted on the negative electrode 13, and the positiveelectrode (air electrode) 15 on which the lithium ion conductive solidelectrolyte membrane is disposed, is mounted on the opposite side of thecase 11 to face the negative electrode 13. Subsequently, the firstcurrent collector 14 is disposed on the positive electrode (airelectrode) 15, and the pressing member 19 allowing air to reach thepositive electrode (air electrode) 15 is pressed to fix a cell, therebycompleting preparation of the lithium air battery 10.

If desired, a small amount of a liquid electrolyte including a lithiumsalt may be injected into the separator mounted on the negativeelectrode during preparation of the battery. For example, the separatormay be impregnated with a 1.0 molar (M) lithium trifluoromethanesulfonimide (LiTFSI) propylene carbonate electrolytic solution, but isnot limited thereto, and the separator may include an aprotic organicsolvent and a lithium salt, or an ionic liquid and a lithium salt insmall amounts.

Examples of the aprotic solvent may include propylene carbonate,ethylene carbonate, fluoroethylene carbonate, butylene carbonate,dimethyl carbonate, diethyl carbonate, methylethyl carbonate,methylpropyl carbonate, ethylpropyl carbonate, methylisopropylcarbonate, dipropyl carbonate, dibutyl carbonate, benzonitrile,acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone,dioxolane, 4-methyldioxolane, N,N-dimethylformamide,N,N-dimethylacetamide, dimethylsulfoxide, dioxane, 1,2-dimethoxyethane,sulfolane, dichloroethane, chlorobenzene, nitrobenzene, diethyleneglycol, dimethylether, or any mixture thereof.

Examples of the ionic liquid may include diethylmethyl(2-methoxyethyl)ammonium bis(trifluoromethane sulfonyl) imide(DEME-TFSi).

For example, the ionic liquid may be a polymeric ionic liquid. Thepolymeric ionic liquid may include a repeating unit including: i) atleast one cation including ammonium, pyrolidium, pyridinium, pyrimidium,imidazolium, piperidinium, pyrazolium, oxazolium, pyrazinium,phosphonium, sulfonium, triazolium, or any mixture thereof, and ii) atleast one anion including BF₄ ⁻, PF₆ ⁻, AsF₆ ⁻, SbF₆ ⁻, AlCl₄ ⁻, HSO₄ ⁻,ClO₄ ⁻, CH₃SO₃ ⁻, CF₃CO₂ ⁻, (CF₃SO₂)₂N⁻, Cl⁻, Br⁻, I⁻, BF₄ ⁻, SO₄ ²⁻,PF₆ ⁻, ClO₄ ⁻, CF₃SO₃ ⁻, CF₃CO₂ ⁻, (C₂F₅SO₂)₂N⁻, (C₂F₅SO₂)(CF₃SO₂)N⁻,NO₃ ⁻, Al₂Cl₇ ⁻, AsF₆ ⁻, SbF₆ ⁻, CF₃COO⁻, CH₃COO⁻, CF₃SO₃ ⁻,(CF₃SO₂)₃C⁻, (CF₃)₂PF₄ ⁻, (CF₃)₃PF₃ ⁻, (CF₃)₄PF₂ ⁻, (CF₃)₅PF⁻, (CF₃)₆P⁻,SF₅CF₂SO₃ ⁻, SF₅CHFCF₂SO₃ ⁻, CF₃CF₂(CF₃)₂CO⁻, (CF₃SO₂)₂CH⁻, (SF₅)₃C⁻,(O(CF₃)₂C₂(CF₃)₂O)₂PO⁻, (CF₃SO₂)₂N⁻, or any mixture thereof.

The case may be divided into a lower portion contacting the negativeelectrode and an upper portion contacting the air electrode. Aninsulating resin may be interposed between the upper and lower portionsto electrically insulate the air electrode and the negative electrodefrom each other.

There is no need to further dispose the lithium ion conductive polymerelectrolyte between the negative electrode 13 and the positive electrode(air electrode) 15. Thus, the total weight of the lithium air batterymay be reduced, thereby improving energy density per unit weight.

The lithium air battery may be either a lithium primary battery or alithium secondary battery. The lithium air battery may be any of variousforms, and for example, may be in the form of a coin, a button, a sheet,a stack, a cylinder, a plane, or a horn, without limitation. Also, thelithium air battery may be applied to a large battery for electricvehicles.

The term “air” used herein is not limited to atmospheric air, and mayalso refer to a combination of gases including oxygen or pure oxygengas. This broad definition of “air” also applies to other terms,including an air battery, air positive electrode, and the like.

A method of preparing a positive electrode for a metal air batteryaccording to another example embodiment may include preparing thepositive electrode including the carbonaceous material and a coating ona surface of the carbonaceous material, the coating including thepolymer electrolyte layer including the polymer electrolyte comprised ofat least one type of hydrophilic material and at least one type ofhydrophobic material. The preparing of the positive electrode includesadding the carbonaceous material, the polymer electrolyte, and thelithium salt to a solvent, dispersing the carbonaceous material, thepolymer electrolyte, and the lithium salt in the solvent to prepare adispersion, and drying the dispersion.

The carbonaceous material, the polymer electrolyte, and lithium salt areas described above, and thus further descriptions thereof will not begiven.

For example, the solvent may include water, alcohol, acetone,tetrahydrofuran, cyclohexane, carbon tetrachloride, chloroform,methylene chloride, dimethyl formamide, dimethylacetamide, dimethylsulfoxide, N-methylpyrolidone, or a combination thereof.

FIG. 2 is a schematic diagram describing a method of preparing apositive electrode for a metal air battery according to an exampleembodiment.

A carbonaceous material and a polymer electrolyte are added to a solventin an appropriate weight ratio to obtain a mixture. A lithium salt(e.g., LiTFSI) is added thereto and dispersed in an appropriate molarratio of polymer electrolyte monomers to lithium ions. Then, theresulting dispersion may be filtered before being dried. A filteringprocess may be performed using a filter including pores having a porediameter of 1 micrometer (μm) or less. For example, the filteringprocess may be performed using a PVdF membrane. Through this process, acarbonaceous material including the lithium salt and having a polymerelectrolyte coating layer on the surface thereof may be obtained.

The method may further include a crosslinking process after adding thecarbonaceous material, the polymer electrolyte, and the lithium salt tothe solvent, dispersing the mixture, and drying the dispersion.

The crosslinking process may be a thermal crosslinking process or anultraviolet (UV) crosslinking process. If desired, a crosslinking agentmay be used in the thermal crosslinking process, and a UV initiator maybe used in the UV crosslinking process.

For example, the crosslinking agent may be a polyhydric alcohol or apolyvalent epoxy compound. Examples of the polyhydric alcohol mayinclude an aliphatic polyhydric alcohol such as ethylene glycol,glycerin, and polyvinyl alcohol, and an aromatic polyhydric alcohol suchas pyrocatechol, resorcinol and hydroquinone. Examples of the polyvalentepoxy compound may include an aliphatic polyvalent epoxy compound suchas glyceryl polyglycidyl ether and trimethylolpropane polyglycidylether, and an aromatic polyvalent epoxy compound such as a bisphenolA-type epoxy compound. However, the crosslinking agent is not limitedthereto, and any suitable crosslinking agent may be used. By using thecrosslinking agent, crosslinking density may be easily adjusted and thepolymer electrolyte layer including the polymer electrolyte may beefficiently anchored to the surface of the carbonaceous material.

An amount of the crosslinking agent may be about 1% to about 40% byweight based on a total weight of polymerizable monomers of the polymerelectrolyte.

The thermal crosslinking may be performed under atmospheric conditionsor oxidation conditions at a temperature of about 80° C. to about 120°C. for about 2 hours to about 6 hours.

The UV initiator may be any material capable of generating free radicalsupon exposure to UV light, without limitation. For example, the UVinitiator may have a double bond. The carbonaceous material having thepolymer electrolyte coating layer on the surface thereof may be exposedto UV light for about 20 minutes to about 60 minutes using a UVirradiator to perform UV crosslinking.

Then, the unreacted crosslinking agent or the unreacted UV initiator areremoved from the vacuum oven to prepare a positive electrode for a metalair battery.

Hereinafter, one or more example embodiments of the present disclosurewill be described in detail with reference to the following examples andcomparative examples. These examples and comparative examples are notintended to limit the purpose and scope of the one or more exampleembodiments of the present inventive concept.

EXAMPLES Example 1: Preparation of Carbonaceous Material Coated withPolymer Electrolyte Layer

50 mg of multi-walled carbon nanotubes (Hanwha Chemical, CM250, 92-96%purity) and 200 mg of a polyethylene glycol-b-polypropyleneglycol-b-polyethylene glycol triblock copolymer (Sigma Aldrich, PluronicP-123, average Mn: 5800 Da, ethylene oxide: propylene oxide: ethyleneoxide (EO:PO:EO) feed ratio=20:70:20, PEG: 30% by weight), as a polymerelectrolyte, were added to 100 mL of water to prepare a mixture.

Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) powder was added tothe mixture such that a molar ratio of EO/Li was 20:1 and the mixturewas dispersed using a sonicator for 2 hours. A predetermined amount ofthe dispersion was filtered using a Whatman® PVdF membrane (pore size:0.2 μm) to prepare multi-walled carbon nanotubes coated with the polymerelectrolyte layer including the PEG-b-PPG-b-PEG triblock copolymerpolymer electrolyte.

The resultant was dried at room temperature for 12 hours and in a vacuumoven for 12 hours. Then, the dried resultant was impregnated with anexcess of a UV initiator, Luperox® 104, to perform UV crosslinking. Theunreacted Luperox® 104 UV initiator was removed from the vacuum oven toprepare multi-walled carbon nanotubes coated with a polymer electrolytelayer comprised of the crosslinked PEG-b-PPG-b-PEG triblock copolymerpolymer electrolyte.

Example 2: Preparation of Carbonaceous Material Coated with PolymerElectrolyte Layer

Multi-walled carbon nanotubes coated with a polymer electrolyte layerwere prepared in the same manner as in described Example 1 except that apolyethylene glycol-b-polypropylene glycol-b-polyethylene glycoltriblock copolymer (Sigma Aldrich, Pluronic F-127, average Mn: 12,100Da, EO:PO:EO=101:56:101 feed ratio, PEG: 73.5% by weight) was used asthe polymer electrolyte instead of the polyethyleneglycol-b-polypropylene glycol-b-polyethylene glycol triblock copolymer(Sigma Aldrich, Pluronic P-123, average Mn: 5800 Da, EO:PO:EO feedratio=20:70:20, PEG: 30% by weight).

Example 3: Preparation of Lithium Air Battery

A separator (Celgard 3501) was disposed on a lithium metal thin filmnegative electrode.

0.1 mL of an electrolyte prepared by dissolving 1 M lithiumbis(trifluoromethanesulfonyl)imide (LiTFSI) in poly(ethyleneglycol)-dimethylether (Sigma Aldrich, Mw: 500 Da) was injected into theseparator.

As a solid electrolyte, a lithium-aluminum titanium phosphate (LATP,thickness: 250 μm, Ohara Corp., Japan) was disposed on the separator.

Then, the multi-walled carbon nanotubes coated with the polymerelectrolyte layer comprised of the crosslinked PEG-b-PPG-b-PEG triblockcopolymer polymer electrolyte and prepared according to Example 1, wasdisposed on the LATP solid electrolyte as a positive electrode (airelectrode). In this case, the amount of the multi-walled carbonnanotubes coated with the polymer electrolyte layer was 90.5 parts byweight and the amount of the lithium salt was 9.5 parts by weight basedon 100 parts by weight of the air electrode.

Then, a gas diffusion layer (GDL, SGL, 25BC) was attached to the uppersurface of the positive electrode, a nickel mesh was disposed on the gasdiffusion layer, and a pressing member allowing air to reach thepositive electrode was applied thereto to fix a cell, thereby completingpreparation of a lithium air battery.

A structure of the lithium air battery according to an exampleembodiment is illustrated in FIG. 3.

Example 4: Preparation of Lithium Air Battery

A lithium air battery was prepared in the same manner as described inExample 3, except that the multi-walled carbon nanotubes coated with thepolymer electrolyte layer prepared according to Example 2 was used asthe positive electrode (air electrode) instead of the multi-walledcarbon nanotubes coated with the polymer electrolyte layer preparedaccording to Example 1.

Comparative Example 1: Preparation of Lithium Air Battery (1)Preparation of Positive Electrode (Air Electrode)

An electrolyte was prepared by mixing polyethylene oxide (average Mn:100,000 Da, Aldrich), as an ion conductive polymer, with LiTFSI, as alithium salt, on a hot plate such that a molar ratio of EO/Li was 20.Multi-walled carbon nanotubes (Hanwha Chemical, CM250, 92-96%) wereadded to the electrolyte such that a weight ratio of the electrolyte tothe multi-walled carbon nanotubes was 3:1, and then mixed to prepare apositive electrode (air electrode) slurry.

The air electrode slurry was coated on a LATP solid electrolyte layer(thickness: 250 μm, Ohara Corp., Japan) such that an amount of the airelectrode slurry used to prepare a positive electrode (air electrode)was 3.248 mg/cm² (about an area of 1 cm×1 cm).

(2) Preparation of Lithium Air Battery

A lithium air battery was prepared in the same manner as in Example 3,except that the positive electrode (air electrode) prepared according topreparation (1) above was used as a positive electrode instead of themulti-walled carbon nanotubes coated with the polymer electrolyte layerprepared according to Example 1.

Analysis Example 1: TEM Analysis—Morphology Analysis

The carbonaceous materials coated with the polymer electrolyte layersrespectively prepared according to Examples 1 and 2 were analyzed usingTEM images. The TEM analysis was performed using a Titan Cubed G2 60-300microscope manufactured by FEI. The results are shown in FIGS. 4A to 4C.

FIGS. 4A and 4C are TEM images of the carbonaceous materials coated withthe polymer electrolyte layers prepared according to Examples 1 and 2.FIG. 4B is a TEM image of the carbonaceous material coated with thepolymer electrolyte layer prepared according to Example 2.

Referring to FIGS. 4A and 4C, it was confirmed that the polymerelectrolyte layers prepared according to Examples 1 and 2 were formed onthe surfaces of the carbonaceous materials at thicknesses of about 2 nm,and about 5 nm to about 10 nm, respectively (bidirectional arrows).

Referring to FIG. 4B, it was confirmed that all or a portion of thepolymer electrolyte of the polymer electrolyte layer was anchored to andcrosslinked with the surface of the carbonaceous material of Example 2.The anchoring was facilitates via noncovalent and/or covalent bonds.

Analysis Example 2: TGA—Weight Reduction Rate of Polymer Electrolyte

The polymer electrolyte layer of the carbonaceous material coated withthe polymer electrolyte layer prepared according to Example 1 wasanalyzed and identified by thermal gravimetric analysis (TGA).

The TGA was performed by measuring, using a thermogravimetric analyzer(Q5000 manufactured by TA Instruments), weight loss of 10 mg of a sampleof the carbonaceous material while its temperature increased from 0° C.to 800° C. at a rate of 10° C./min in a nitrogen atmosphere. The resultsare shown in FIG. 5.

Referring to FIG. 5, weight reduction of the polymer electrolyte startedat about 330° C. and stopped at about 400° C. It was confirmed that thelevel of weight reduction of the polymer electrolyte was about 45.5%.

Analysis Example 3: XPS Analysis—Analysis of Polymer Electrolyte Layeron Surface of Carbonaceous Material

The carbonaceous material coated with the polymer electrolyte layerprepared according to Example 2 was analyzed by X-ray PhotoelectronSpectroscopy (XPS) to identify the polymer electrolyte of the polymerelectrolyte layer. The results are shown in FIGS. 6A and 6B.

The XPS was performed using an appropriate amount of a sample of thecarbonaceous material using an X-ray photoelectron spectrometer (PHI,Versaprobe).

Referring to FIG. 6A, C—O bonds were observed in the polymer electrolytecoated on the surface of the carbonaceous material and C—C bonds and C═Cbonds were observed between the carbonaceous material and the polymerelectrolyte. After sputtering for 2 minutes, the surface of thecarbonaceous material was pulverized and observed by XPS. The resultshowed a peak corresponding to the C—O bonds was reduced.

Referring to FIG. 6B, a decrease in the peak corresponding to the C—Obonds was observed after sputtering for 2 minutes. Thus, it wasidentified that the polymer electrolyte is coated on the surface of thecarbonaceous material.

Evaluation Example 1: Evaluation of Charge and DischargeCharacteristics—Evaluation of Energy Density

The lithium air batteries prepared according to Example 3 andComparative Example 1 were discharged at a constant current of 0.048mA/cm² at 60° C. and at 1 atm in an oxygen atmosphere until a voltagereached 2.0 V (vs. Li) and charged at the same current until the voltagereached 4.3 V; charging was performed at this voltage until the chargingcurrent reached 0.0048 mA/cm². The part of results of charging anddischarging tests at a first cycle are shown in Table 1 and FIG. 7A.

Also, the lithium air batteries prepared according to Example 4 andComparative Example 1 were discharged at a constant current of 0.048mA/cm² at 60° C. and at 1 atm in an oxygen atmosphere until a voltagereached 2.0 V (vs. Li) and charged at the same current until the voltagereached 4.3 V; charging was performed at this voltage until the chargingcurrent reached 0.0048 mA/cm². The part of results of charging anddischarging tests at a first cycle are shown in Table 2 and FIG. 7B.

In the energy density per unit weight, the unit weight is a total weightof the positive electrode including the electrolyte, the carbonaceousmaterial (coated with the polymer electrolyte layer), and the dischargeproducts, and the energy density is obtained by dividing a product of adischarge amount and an average discharge voltage by the weight.

TABLE 1 Weight of Weight of Discharge Energy carbon electrolyte amountdensity (mg) (mg) (mAh) (Wh/kg) Example 3 0.40645 0.33255 0.43 190.18Comparative 0.406 1.218 0.43 145.81 Example 1

TABLE 2 Weight of Weight of Discharge Energy carbon electrolyte amountdensity (mg) (mg) (mAh) (Wh/kg) Example 4 1.03 0.499 0.54 237.12Comparative 1.03 3.10 0.54 164.97 Example 1

Referring to Table 1 and FIG. 7A, energy density of the lithium airbattery prepared according to Example 3 was higher than that of thelithium air battery prepared according to Comparative Example 1 by about44 Wh/kg. Referring to Table 2 and FIG. 7B, energy density of thelithium air battery prepared according to Example 4 was higher than thatof the Comparative Example 1 by 72 Wh/kg. These results are aconsequence of the weight of the electrolyte being reduced in thepositive electrode (air electrode) of the lithium air battery.

The positive electrode for a metal air battery according to an exampleembodiment includes the lithium salt, the carbonaceous material, and acoating on a surface of the carbonaceous material, the coating includingthe polymer electrolyte coating layer including the polymer electrolyteincluding at least one type of hydrophilic material and at least onetype of hydrophobic material. Since a portion of the polymer electrolyteis anchored to the surface of the carbonaceous material via anoncovalent and/or covalent bond, an amount of the electrolyte may bereduced. The metal air battery including the positive electrode for ametal air battery may have increased energy density per unit weight.

It should be understood that example embodiments described herein shouldbe considered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each exampleembodiment may be considered as available for other similar features oraspects in other embodiments.

While one or more example embodiments have been described with referenceto the figures, it will be understood by those of ordinary skill in theart that various changes in form and details may be made therein withoutdeparting from the spirit and scope as defined by the following claims.

What is claimed is:
 1. A positive electrode for a metal air battery, thepositive electrode comprising: a lithium salt; a carbonaceous material;and a coating on a surface of the carbonaceous material, the coatingcomprising a polymer electrolyte comprising a hydrophilic material and ahydrophobic material, wherein a portion of the polymer electrolyte isanchored to the surface of the carbonaceous material by a chemical bond,wherein the polymer electrolyte comprises a block copolymer comprising ahydrophobic block comprising the hydrophobic material and a hydrophilicblock comprising the hydrophilic material, and wherein the hydrophobicmaterial comprises a hydrophobic repeating unit consisting of butylacrylate, 2-ethylhexyl acrylate, methacrylate, benzyl methacrylate,butyl methacrylate, tert-butyl methacrylate, cyclohexyl methacrylate,2-ethylhexyl methacrylate, hexadecyl methacrylate, hexyl methacrylate,isobutyl methacrylate, isopropyl methacrylate, methyl methacrylate,octadecyl methacrylate, tetrahydrofurfuryl methacrylate, acrylonitrile,maleic anhydride, styrene, propylene glycol, propylene oxide, butene,1-decene, dicyclopentadiene, isobutylene, 4-methyl-1-pentene, ethylene,propylene, ethylene adipate, ethylene succinate, ethylene terephthalate,2-ethyl-1,3-hexanediol sebacate, vinyl acetate, vinyl cinnamate, vinylstearate, tetrahydrofuran, or a combination thereof.
 2. The positiveelectrode of claim 1, wherein a difference between a contact angle withwater of the hydrophilic material and a contact angle with water of thehydrophobic material is 5° or greater.
 3. The positive electrode ofclaim 2, wherein the contact angle with water of the hydrophilicmaterial is about 0° to 70°.
 4. The positive electrode of claim 2,wherein the contact angle with water of the hydrophobic material is 70°or greater.
 5. The positive electrode of claim 1, wherein all or aportion of the hydrophobic material of the polymer electrolyte isanchored to the surface of the carbonaceous material via a noncovalentbond.
 6. The positive electrode of claim 1, wherein all or a portion ofthe hydrophobic material of the polymer electrolyte is adsorbed to thesurface of the carbonaceous material via a Van der Waals' interaction.7. The positive electrode of claim 1, wherein the polymer electrolytecomprises a crosslinked polymer electrolyte.
 8. The positive electrodeof claim 1, wherein the hydrophobic block of the block copolymer isanchored to the surface of the carbonaceous material, and thehydrophilic block is disposed on the surface of and separated from thecarbonaceous material.
 9. The positive electrode of claim 1, wherein theblock copolymer comprises at least two different monomer blocks.
 10. Thepositive electrode of claim 1, wherein the hydrophilic block of theblock copolymer has a number average molecular weight of about 500Daltons to about 20,000 Daltons.
 11. The positive electrode of claim 1,wherein the hydrophilic block is a polymer block having a lithium ionconductive group as a side chain.
 12. The positive electrode of claim11, wherein the polymer block having a lithium ion conductive group as aside chain is a polyacrylate block functionalized with —(CF₃SO₂)₂N⁻, or—(FSO₂)₂N⁻, or a polymethacrylate block functionalized with —(CF₃SO₂)₂N⁻or —(FSO₂)₂N.
 13. The positive electrode of claim 1, wherein the blockcopolymer comprises a polyethylene glycol-b-polypropylene glycol diblockcopolymer, a polyethylene oxide-b-polypropylene oxide diblock copolymer,a polystyrene-b-polyethylene glycol diblock copolymer, apolystyrene-b-polyethylene oxide diblock copolymer, apolystyrene-b-poly(4-vinylpyridine) diblock copolymer, apolystyrene-b-poly(meth)acrylate diblock copolymer, apolystyrene-b-poly(meth)acrylate diblock copolymer functionalized with—(CF₃SO₂)₂N⁻ anion, a polystyrene-b-poly(meth)acrylate diblock copolymerfunctionalized with —(FSO₂)₂N⁻ anion, a polyethyleneglycol-b-polypropylene glycol-b-polyethylene glycol triblock copolymer,a polyethylene oxide-b-polypropylene oxide-b-polyethylene oxide triblockcopolymer, a polyethylene glycol-b-polystyrene-b-polyethylene glycoltriblock copolymer, a polyethylene oxide-b-polystyrene-b-polyethyleneoxide triblock copolymer, or a combination thereof.
 14. The positiveelectrode of claim 1, wherein the block copolymer comprises acrosslinked polyethylene glycol-b-polypropylene glycol diblockcopolymer, a crosslinked polyethylene oxide-b-polypropylene oxidediblock copolymer, a crosslinked polystyrene-b-polyethylene glycoldiblock copolymer, a crosslinked polystyrene-b-polyethylene oxidediblock copolymer, a crosslinked polystyrene-b-poly(meth)acrylatediblock copolymer functionalized with —(CF₃SO₂)₂N⁻ anion, a crosslinkedpolystyrene-b-poly(meth)acrylate diblock copolymer functionalized with—(FSO₂)₂N⁻ anion, a crosslinked polyethylene glycol-b-polypropyleneglycol-b-polyethylene glycol triblock copolymer, a crosslinkedpolyethylene oxide-b-polypropylene oxide-b-polyethylene oxide triblockcopolymer, a crosslinked polyethyleneglycol-b-polystyrene-b-polyethylene glycol triblock copolymer, acrosslinked polyethylene oxide-b-polystyrene-b-polyethylene oxidetriblock copolymer, or a combination thereof.
 15. The positive electrodeof claim 1, wherein the block copolymer has a number average molecularweight of about 3,000 Daltons to about 60,000 Daltons.
 16. The positiveelectrode of claim 1, wherein an amount of the polymer electrolyte isabout 10 parts by weight to about 300 parts by weight based on 100 partsby weight of the carbonaceous material.
 17. The positive electrode ofclaim 1, wherein the polymer electrolyte layer has thickness of about 1nanometer to about 30 nanometers.
 18. The positive electrode of claim 1,wherein the polymer electrolyte layer is electrochemically stable withrespect to lithium in a charge/discharge voltage range of about 1.4volts to about 4.5 volts.
 19. The positive electrode of claim 1, whereinthe carbonaceous material comprises a porous carbon structure.
 20. Thepositive electrode of claim 1, wherein the carbonaceous materialcomprises carbon nanotubes, carbon nanoparticles, carbon nanofibers,carbon nanosheets, carbon nanorods, carbon nanobelts, graphene, grapheneoxide, carbon aerogel, inverse opal carbon, or a combination thereof.21. The positive electrode of claim 1, wherein an amount of thecarbonaceous material is about 50 parts by weight to about 80 parts byweight based on 100 parts by weight of the positive electrode.
 22. Thepositive electrode of claim 1, wherein the lithium salt comprises LiPF₆,LiBF₄, LiSbF₆, LiAsF₆, LiN(SO₂C₂F₅)₂, Li(CF₃SO₂)₂N, LiC₄F₉SO₃, LiClO₄,LiAlO₂, LiAlCl₄, LiN(C_(x)F_(2x-1)SO₂)(C_(y)F_(2y-1)SO₂), where x and yare natural numbers, LiF, LiBr, LiCl, LiOH, LiI, LiB(C₂O₄)₂, or acombination thereof.
 23. The positive electrode of claim 1, wherein anamount of the lithium salt is about 5 parts by weight to about 60 partsby weight based on 100 parts by weight of the positive electrode. 24.The positive electrode of claim 1, wherein the positive electrode is anair electrode.
 25. A metal air battery comprising: a negative electrodecomprising lithium or a lithium alloy; the positive electrode accordingto claim 1; and a separator disposed between the negative electrode andthe positive electrode.
 26. A method of preparing the positive electrodefor a metal air battery of claim 1, the method comprising: combining acarbonaceous material, the polymer electrolyte, a lithium salt, and asolvent; dispersing the carbonaceous material, the polymer electrolyte,and the lithium salt in the solvent to prepare a dispersion; and dryingthe dispersion to prepare the positive electrode.
 27. The method ofclaim 26, further comprising performing a filtering process after thedispersing of the carbonaceous material, the polymer electrolyte, andthe lithium salt in the solvent and before drying the dispersion. 28.The method of claim 27, wherein the filtering process is performed usinga filter having pores with a pore diameter of 1 micrometer or less. 29.The method of claim 26, further comprising performing a crosslinkingprocess after the dispersing of the carbonaceous material, the polymerelectrolyte, and the lithium salt in the solvent, and after drying thedispersion.
 30. The method of claim 29, wherein the crosslinking processis a thermal crosslinking process or an ultraviolet light crosslinkingprocess.